1. Field of the Invention
The present invention relates to a process for the preparation of thermoplastic polymer fibers.
2. Description of the Prior Art
Thermoplastic polymer fibers have drawn a lot of attention in view of their very interesting combination of potentially high strength and low weight. For this reason they are being widely used as reinforcement in many applications such as car tyres and structural applications.
It is generally accepted that for a given polymer the performance properties of the fibers prepared therefrom are amongst others related to the degree of stretching, hereinafter referred to as the draw-ratio, which can be achieved when stretching the spun fibers, which ratio may be enhanced by a high degree of polymer molecule disentanglement.
The process generally used for the preparation of thermoplastic polymer fibers, having performance properties as described hereinbefore, is solution- or gel-spinning. These processes differ from the melt-spinning process in that the polymers are dissolved in a suitable solvent or solvent blend prior to being spun, which dissolving step promotes disentanglement of the polymer molecules. A further difference from the melt-spinning process is that the solution or gel-spinning processes permit the processing of considerably higher molecular weight polymers, which is considered to be an additional advantage for the fiber production, as it is known that a high molecular weight can have a beneficial effect on the mechanical properties of products based thereon.
It has been reported by J. Smook et al, in a Poster presentation at the Rolduc Abbey Polymer Meeting, April 26-30 1987, in The Netherlands, that contrary to the excellent results obtained with gelspun ultra high molecular weight polyethylene, e.g. a maximum draw ratio=80, similar experiments with polar polymers, such as polyamides and polyesters, only resulted in draw ratios which were very similar to those obtained with the corresponding melt-spun fibers, i.e. draw ratio=6-7. These results indicate that there is still further need for improvement n the preparation of thermoplastic polymer fibers based on polar polymers, especially as fibers based on polar polymers generally demonstrate superior adhesion characteristics compared to fibers based on non-polar polymers, such as polyolefin-based fibers.